1. Field of the Invention
The present invention relates to a protective jacket for holding a plane disc magnetic recording medium.
2. Description of the Prior Art
Plane magnetic recording media have been widely used as recording media in data processing apparatus, and have been prepared by coating a magnetic varnish on a substrate made of polyester etc. to form a magnetic layer as in the conventional magnetic tape.
The plane magnetic recording medium has been held in a protective jacket so as to protect the recording surface thereof and to reinforce the flexible substrate and it is rotated in the protective jacket to write in or to read out data.
FIGS. 1 and 2 show the conventional protective jackets. FIG. 1 is a sectional plane view and FIG. 2 is a sectional view taken along A--A line of FIG. 1.
As shown in FIGS. 1 and 2, the conventional protective jacket comprises a central opening (2) and a head inserting opening (3) on the central part of a jacket body which is formed by sealing all of peripheral sides; and buffer sheets (4) such as nonwoven sheets which are bonded on both inner surfaces of the jacket body (1) in linear forms; and a disc magnetic recording medium (5) which is held between the buffer sheets (4) in linear forms.
In the conventional protective jacket, the buffer sheets (4) are heat-bonded in the linear forms on the inner walls at bonding parts a, b, c, d and e except the central opening (2) and the head inserting opening (3).
In this structure, the surfaces a, b, c, d and e of the buffer sheets (4) are lower than the non-bonding parts to form gaps between the surfaces of the buffer sheets (4) and the non-bonded inner wall.
Therefore, frictions of the buffer sheets are large and sometimes hooking trouble is caused when the disc magnetic recording medium (5) is rotated in the jacket body (1), whereby the recording surface of the magnetic recording medium (5) is damaged to deteriorate reproducing output characteristics and modulation percentage. Sometimes, it is sufficiently to be useless.